Conventionally, an internal combustion engine (i.e., an engine) having cylinders includes a surge tank, and the surge tank is divided into two chambers, a first surge tank and a second surge tank, by disposing a partition wall. The partition wall includes an opening through which the first surge tank and the second surge tank are communicated with each other. An intake control valve is disposed at the opening. The intake control valve has a valve part (e.g., a butterfly valve). When the butterfly valve is fully closed, the first surge tank and the second surge tank are separated from each other. When the butterfly valve is fully open, the first surge tank and the second surge tank are communicated with each other. Such variable intake system is described in, for example, patent document 1 (JP No. 4053393 corresponding to US 2004/0055565 A1).
The intake control valve has a valve holder. The valve holder will be referred to as a valve body hereafter. The valve body includes a valve hole passing through the valve holder. The butterfly valve includes a shaft holder to which a shaft is inserted. The shaft holder is rotatably disposed in a bearing of the valve body such that the valve hole is opened or closed by moving the shaft. The valve body having the butterfly valve is inserted in the opening of the surge tank.
According to the intake control valve described in patent document 1, the shaft is inserted in the shaft holder. A recessed portion of the butterfly valve and a valve holding portion of the shaft are fitted to each other, and the butterfly valve is fastened to the shaft by a bolt. Therefore, the number of components and man-hour are large, and cost increases.
Then, a shaft may be press-fitted to a butterfly valve made of synthetic resin, as described in patent document 2 (JP No. 4901016), to reduce the number of components and man-hour so as to reduce cost.
According to an intake control valve described in patent document 2, the butterfly valve is integrally formed with a shaft holder and bearings. The shaft holder is located at a center portion of the butterfly valve, and the shaft is fixed to the shaft holder. One of the bearings is located at an end side of the butterfly valve in a rotation axial direction of the butterfly valve, and the other bearing is located at another end side of the butterfly valve facing the one end side in the rotation axial direction. The bearings rotate and slide relative to bearing holders provided in the valve body of an intake manifold.
According to the above structure, since the valve body has the bearings, bearings holding the butterfly valve are not provided. In this case, a location of the butterfly valve is not set with respect to the valve hole of the valve body. Accordingly, the shaft cannot be press fitted in the shaft holder of the butterfly valve. In the result, specific bearing holders described in patent document 2 are required.